1. Field of the Invention
The present invention relates to a display controller for CRT flat panel devices, such as and plasma display apparatuses.
2. Description of the Related Art
Along with the development of microcomputers, a variety of personal computers have been developed. The display apparatuses of such microcomputers may employ flat panel display device such as a plasma display apparatus (PDP). The PDP is controlled by a display controller for a CRT display apparatus (to be referred to as a CRT controller hereinafter).
On the other hand, a cathode ray tube (CRT) display apparatus is widely used as a display apparatus. Therefore, a variety of application programs have been developed in which output data is generated for the CRT display apparatus. A demand has arisen for effective use of such software resources. That is, a PDP is used as a main display apparatus, and a CRT display apparatus is connected as an option, so that the two types of display apparatuses are selectively used in accordance with application programs. In this case, when data from an application program for a CRT display apparatus is to be displayed using a PDP, color display is sometimes disturbed.
In some apparatuses, gradation (that is, variation in gray scale) of a PDP is altered to display color data. However, when gradation display is performed in a conventional PDP, display picture elements, or dots, are thinned or adjacent dots are turned on/off to reduce the gradation level to 1/2, thereby altering the gradation. However, such a pseudo gradation display means cannot alter gradation in correspondence with different color data.
When color data originally generated for display on a color display are displayed on PDP by altering, gradation and when such color data is displayed on CRT under control of a single display controller, if display luminance levels of the CRT are directly used in a PDP without modification, the following problems are posed.
More specifically, the luminance of a PDP is normally lower than that of a CRT. Therefore, if the luminance level of the PDP is set to be higher than a normal value as in the luminance of the CRT, the luminance of normal display is decreased, thus making it difficult to see a display screen.